In epitaxial growth of a silicon wafer, for the purpose of enhancing an outer periphery resistivity distribution or improving appearance of a back surface, a susceptor having through holes that penetrate to reach a susceptor back surface and are opened is often used (See Patent Document 1). Although the through holes provided in the susceptor have achieved various kinds of quality improvement, local depositions on an outer peripheral portion of a wafer back surface (hereinafter, referred to as “back surface depositions”) are also produced.
Usually, a raw-material gas is allowed to flow to a wafer front side. The raw-material gas sometimes then flows into the back surface of the susceptor because of a mechanism of an epitaxial manufacturing apparatus. The raw-material gas that has flowed into the back surface side of the susceptor then flows into the back surface side of the wafer via the through holes of the susceptor and reacts on the back surface of the wafer; thus the back surface depositions are generated.
At this time, the back surface depositions of the wafer are locally generated in the vicinity of a contact portion of the susceptor and the wafer, i.e., an outer peripheral portion of the wafer back surface (in the case of a wafer having a diameter of 300 mm, a portion that is approximately 147 to 149 mm in radius from the center of the wafer), and a height thereof varies in accordance with a reaction time, but it reaches several hundred nanometers.
When flatness of the epitaxial wafer on which the back surface depositions have been produced is measured on the basis of the position of the back surface, the thickness of the epitaxial wafer precipitously increases at the outer peripheral portion, which results in flatness deterioration. In recent years, devices are miniaturized and high flatness is demanded even for a wafer outer peripheral portion, the back surface depositions can be a considerable obstacle for manufacture of latest products.
In conventional examples, the back surface depositions are intensively produced in a portion where a wafer and a susceptor are in contact with each other or they closely overlap each other, namely, a margin for mounting the susceptor, a back surface deposition height fluctuates in accordance with a thermal dose on the susceptor side, and hence a method for reducing the margin for mounting the susceptor as much as possible, a method for enlarging the margin for mounting the susceptor and continuously generating the back surface depositions, or a method for reducing lamp heating using a lamp on the lower side of the susceptor is mainly adopted in order to cope with the problem.
However, the above-described methods are effective for the back surface depositions, but they have drawbacks, e.g., slip dislocation is apt to occur, nano-topology quality on a front side is deteriorated, or outer periphery resistivity distribution quality is deteriorated.
Furthermore, Patent Document 2 discloses that a protrusion is provided at a position corresponding to a wafer outer peripheral portion on a susceptor back side, a heat capacity of the susceptor is increased, a heat keeping effect is enhanced, the wafer outer peripheral portion is heated, and occurrence of slip dislocation is thereby suppressed.